1. Field of the Invention
The present invention relates generally to a rolling mill having a roll arrangement in which working rolls are respectively shifted along the axes thereof in accordance with various rolling conditions and more particularly to a rolling mill used for rolling hot strip materials having a roll arrangement in which the respective working rolls are provided with working-roll bending devices and reinforcing rolls for supporting the working rolls.
2. Description of the Prior Art
In the field of rolling production, there has recently been a strong demand for schedule free rolling and improvements in the quality of rolled products. In response to this demand, the accuracy of thickness of rolled sheet material in its longitudinal direction has been improved to a significant degree by virtue of the development of automatic sheet thickness control. As a known example, U.S. Pat. No. 3024679 discloses a working roll bending method adapted for quadruple rolling mills. this method has been proposed as a means for improving the accuracy of thickness (flatness) of rolled sheet materials in the widthwise direction. The prior art devices, however, have not yet succeeded in ensuring a sufficient degree of accuracy in controlling the thickness of rolled sheet materials in the widthwise direction. For this reason, it is a common practice for a certain degree of deterioration of product shape to be permitted as being unavoidable. Alternatively a multiplicity of working rolls having different initial crowns can be prepared in correspondence with the widths of the specific rolled sheet materials. Employing these methods leads to a deterioration in the quality of rolled products and to an increase in the unit price thereof.
In order to solve the above-described problems, U.S. Pat. No. 3,857,268 discloses a rolling mill having a roll arrangement in which the working rolls are adapted to be shifted along their axes for adjustment purposes in accordance with rolling conditions (e.g., the width of a sheet material to be rolled). The adjustment shift is combined with working-roll bending, to present a reasonable solution to the problem of rolled sheet materials being of irregular thicknesses even if the width of the sheet materials vary in a diverse manner.
Utilization of the working roll shift type rolling mill mentioned above as prior art enables the provision of schedule free rolling. Conventionally, in the case of a hot strip rolling mill, working rolls are subjected to unbalanced abrasion owing to the presence of the lateral edges of the rolled sheet material and there is, therefore, a limit to the number of sheet materials of the same width which can be rolled. In addition, the presence of this unbalanced abrasion unavoidably leads to choosing a rolling method referred to as "coffin schedule" in which sheet materials are rolled with the widths of the rolled products progressively narrowing. The aforesaid schedule free rolling is a method capable of eliminating the above-described limitation of the prior art. According to this schedule free rolling, it is possible not only to freely obtain rolled products having a required width as occasion demands, but also to couple a rolling mill directly to production facilities that are disposed upstream of the rolling mill for producing sheet materials to be rolled. Therefore, this feature enables effective utilization of thermal energy, thereby leading to the advantage that the production cost of the rolled products can be lowered.
As disclosed in the above cited U.S. Pat. No. 3,857,268, if an existing quadruple rolling mill for rolling hot strip materials is modified so that working rolls thereof may be shifted along their axes, the thickness of rolled sheet materials can be controlled with an adequate degree of accuracy in their widthwise direction, and it is also possible to provide schedule free rolling that imposes no limitation on the width range of sheet materials to be rolled.
However, in cases where hydraulic actuators for effecting working-roll bending are fixedly disposed on the housing of a rolling mill of the above-described working roll in the same manner as conventional rolling mills, the construction becomes such that hydraulic cylinders are disposed on blocks protruding into a window provided in the housing, the ( blocks being called "projecting blocks". In such cases, the presence of the projecting blocks serve to limit the performance of roll-changing the back-up rolls.
More specifically, although in the case of changing the rolls of a quadruple rolling mill, the changing of the working rolls is not time-consuming, when it comes to the reinforcing rolls. An old reinforcing roll needs to be lifted vertically in the housing to a predetermined position at which roll changing can be undertaken by engaging one end of the old roll with a roll changing C hook suspended from a crane. The old roll to be changed is then shifted from this roll changing position in the direction of its axis, and is thus removed from the housing. Then, a new reinforcing roll is placed in the housing in the reverse order.
However, if the projecting blocks having the hydraulic cylinder for effecting working-roll bending protrude into the window in the housing as in the case of rolling mills having the above-described arrangement, the presence of these projecting blocks causes difficulties when lifting the old reinforcing roll by means of the C hook. For this reason, each time the reinforcing rolls are changed, the projecting blocks must be disassembled and removed from the housing so as to allow the reinforcing rolls to be lifted. In consequence, changing of the reinforcing rolls requires a long period of time and the rolling must be brought to a halt during this changing operation.
In particular, if a rolling mill is of the hot strip rolling mill type, the stoppage of rolling necessitated by the aforesaid changing of the reinforcing rolls has a significant influence. A typical steelworks is only equipped with a single hot strip rolling mill. Accordingly, if the changing of the reinforcing rolls brings the operation of the hot strip rolling mill to a halt for a prolonged period, this has adverse results on the operating of various facilities disposed upstream and downstream of the mill.